A large and growing number of people suffer from diabetes mellitus and obesity. Diabetes mellitus is a metabolic disorder in which the ability to utilize glucose is partly or completely lost.
A number of treatment regimes target excessive blood glucose whereas others are focused primarily on weight reduction. The most efficient anti-diabetic agent used to lower blood glucose is insulin and analogue(s) thereof. It has been known for a long time that when traditional insulin is used to treat diabetes, it is associated with an increase in body weight. Insulin has to be injected subcutaneously up to several times per day.
Type 2 diabetes is generally treated in the early phases with diet and exercise. As the condition progresses, various oral anti-diabetic agents are added. Injected agents such as GLP-1 analogues may also be used at this stage. In general, these agents are most efficient in patients with functioning beta-cells capable of releasing insulin and amylin.
Human amylin (SEQ ID No: 1) is a 37 amino acid long polypeptide which has physico-chemical properties that make its use as a drug troublesome. In particular, it has a tendency for fibrillogenesis, i.e. the formation of fibrils, in vitro and/or ex vivo and becomes ineffective due to precipitation. Additionally amylin is difficult to formulate as it is chemically unstable and it precipitates at physiologic pH. Therefore it is formulated in acidic solution.
Human amylin binds to two distinct receptor complexes. These two complexes contain the calcitonin receptor plus a receptor activity-modifying proteins, RAMP1 or RAMP3. From the close relationship between the calcitonin receptor and the amylin receptor some cross-reactivity to the calcitonin receptor may be expected of amylin receptor agonist. As an example pramlintide has some affinity to the calcitonin receptor but is 14 times more potent on the amylin receptor.
The calcitonin receptor is found in many tissues throughout the body and it is believed to be involved in regulation of bone metabolism. Salmon calcitonin is currently sold under the tradename Miacalcic®. The product is used against hypercalcaemia, osteoporosis (including post-menopausal osteoporosis and glucocorticoid-related osteoporosis), ostitis derformans (Pagets disease) and is administered once daily either by injection or nasally. The calcitonin is bound to specific receptors in the membrane of the skeleton, the kidneys and in the central nervous system (CNS). The plasma half-life for salmon calcitonin is about 45 minutes.
Polypeptides with activity at the calcitonin receptor could be useful in the treatment of hypercalcaemia, osteoporosis, Pagets disease, obesity or obesity related diseases as well as in the prevention of obesity related diseases. A drawback of the treatment with currently used calcitonin preparations are that, due to the short plasma half-life for salmon calcitonin, the drug has to be administered several times a day and has to be administered immediately before a meal.
Polypeptides with dual activity at both the calcitonin receptor and the amylin receptor may be advantageous.
Pramlintide (SEQ ID No: 2) is a drug product marketed by Amylin Pharmaceuticals as Symlin® for the treatment of diabetes as an add-on to insulin. Pramlintide is an amylin receptor agonist. It is approximately 14 times less active on the calcitonin receptor.
The chemical structure of pramlintide is presented below and also in FIG. 1.

Pramlintide is chemically unstable at neutral pH and it is therefore provided in an acidic solution. Compared to human amylin, the amino acids in position 25, 28 and 29 in pramlintide are substituted with proline. This modification reduces the tendency of the protein for fibrillogenesis. Pramlintide has a very short plasma half-life and therefore has to be injected two to three times daily.
WO2010046357 and WO2009034119 disclose polypeptides comprising amylin analogues having an albumin binding residue (called amylin derivatives therein). Even though these polypeptides with albumin binding moieties show improved pharmacokinetic (PK) or pharmacodynamic (PD) properties compared to pramlintide, they may still show poor physical stability under certain conditions.